Many applications of miniature flow sensors require that the flow of air or gas be directed across the sensor in a well-controlled manner. Minature flow sensors can also be practically applied to measuring differential pressure if they are properly packaged in an appropriate housing.
For practical differential pressure application, the rate of flow through the sensor housing should be regulated to low levels to allow effective use of reasonable filters. Effective filtering is required to remove particulates from the gas to prevent particulate accumulation on the sensor. A lower rate of flow through the housing results in a lower amount of airborne particulates entering the housing and results in less loading of the filter and longer maintenance-free use. Also, high flow impedence facilitates a broader base of practical differential pressure applications as the lower flow rates are more tolerable.
It is also preferred that a practical sensor housing for miniature flow sensors be configured so that the gas flow rate or velocity profile at the active sensing area of the miniature sensor is stable and independent of the flow velocity profile outside the housing. That is, the flow profile at the sensor should be substantially fully developed and substantially independent of the flow profile upstream of the housing inlet.
Miniature flow sensors also require circuitry and electrical connections to circuitry to drive, read-out, signal condition the sensor response, or otherwise operate the sensor.
The present invention provides an integral flow sensor and channel assembly capable of satisfying these requirements. Further, the present invention is capable of satisfying these requirements without the need for secondary packaging to carry the sensor or circuitry. Prior housings involved bonding a minature sensor to a first-level package and electrically connecting the first-level package to a second-level package which supports the associated electronic circuitry. The present invention eliminates the need for the first-level package and, at the same time, provides means for meeting the flow control requirements mentioned above.
The present invention is an integral flow sensor and channel assembly comprising a flow sensor having a sensing element integral to a semiconductor body. The assembly further comprises support structure for supporting the flow sensor, the support structure having a first surface. An enclosed flow channel comprises the first surface formed into a groove running below the sensing element. The flow channel comprises an inlet and an outlet for providing flow across the sensing element. The sensing element is located in the flow channel between the inlet and the outlet. The support structure comprises apparatus for flip-chip mounting the semiconductor body, and the semiconductor body is flip-chip mounted so that the sensing element is positioned over the groove in the support structure.